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Fennel
Foeniculum vulgare
Care level: Easy
Fennel is a tall, airy Mediterranean perennial with thread-fine, feathery leaves and flat heads of small yellow flowers in summer. Every part smells and tastes of aniseed: the leaves go with fish and salads, the flowers and pollen flavour sauces, and the ribbed seeds are a spice for bread, sausages and tea. It grows to 1.8m in sun and well-drained soil, needs almost no care and is a magnet for hoverflies and other insects. Its one fault is that it seeds itself everywhere if the heads are left on.
Foeniculum vulgare 'Purpureum'Foeniculum vulgare var. azoricumFoeniculum vulgare var. dulce
Light
Full sun.
Water
Water young plants until established. Herb fennel then copes with dry spells; Florence fennel needs steady moisture.
Humidity
Not a factor for this outdoor plant.
Soil
Fertile, moist but well-drained soil. Herb fennel also grows in poor, dry ground.
Temperature
Herb fennel is a hardy perennial that dies back in winter and regrows in spring. Florence fennel is grown as an annual.
Size
1.2-1.8m tall and 0.5-1m wide.
?Pet safety not confirmed
As a precaution, keep it out of reach of children and pets.
Did you know?
There are two fennels. Herb fennel is the tall perennial grown for leaves and seeds. Florence fennel is a variety of the same species grown as an annual for its swollen white bulb, and it needs rich soil, steady water and a summer sowing to succeed.
Care by Season
Spring
New shoots rise from the base. Sow herb fennel outdoors once the soil warms.
Summer
Pick leaves freely. Flowers open; sow Florence fennel from early to midsummer.
Autumn
Collect seeds as they turn brown and harvest Florence fennel bulbs before the first frost.
Winter
Herb fennel is dormant below ground. Cut the dead stems down.
Growing & Maintenance
Planting
Sow directly where the plants are to grow, in spring for herb fennel and from early to midsummer for Florence fennel, and thin to 30-45cm apart. One or two plants of herb fennel are enough.
Pruning
Remove fading flower heads to prevent self-seeding and cut the old stems to the ground in late autumn or winter.
Propagation
By seed. Self-sown seedlings can be lifted while tiny.
Pests & Diseases
Common problems
Florence fennel flowers without forming a bulb
Most likely cause: Bolting after cold, drought or root disturbance.
What to do: Sow later, directly in place, and keep the soil moist.
Seedlings all over the garden
Most likely cause: Seed heads left to ripen.
What to do: Deadhead, and hoe off seedlings while small.
Tall stems flop over
Most likely cause: Rich soil, shade or wind.
What to do: Grow in full sun and support with a few canes if needed.
Thin, stringy bulbs
Most likely cause: Dry soil or crowded plants.
What to do: Water regularly and thin to 30cm apart.
The plant wilted after moving
Most likely cause: Damage to the tap root.
What to do: Sow in place next time.
Pests & Diseases
Aphids
Signs: Clusters of small insects on the young shoots and flower heads.
Treatment: Rinse them off with water; hoverflies drawn to the flowers usually clear the rest.
Slugs and snails
Signs: Seedlings and young shoots eaten in spring.
Treatment: Protect seedlings and pick slugs off in the evening.
Powdery mildew
Signs: A white powdery coating on leaves and stems in dry spells late in summer.
Treatment: Water in drought and cut out badly affected stems.
FAQ
What is the difference between herb fennel and Florence fennel?
They are the same species. Herb fennel is a tall perennial with no bulb, grown for leaves, flowers and seeds. Florence fennel forms a fat, white bulb of overlapping leaf bases at ground level and is harvested within a few months of sowing.
Why did my Florence fennel flower instead of making a bulb?
It bolted. Cold nights, drought, root disturbance and sowing too early all trigger flowering. Sow from early to midsummer directly where it is to grow, keep the soil moist and thin the seedlings early.
Does fennel come back every year?
Herb fennel does. It dies down in autumn and shoots again from the base in spring for several years, and it replaces itself with seedlings.
How do I stop it seeding everywhere?
Cut off the flower heads as they fade, before the seeds ripen and drop. If you want seeds for the kitchen, cut the heads when the seeds turn from green to brown and dry them in a paper bag.
Can I move a fennel plant?
Only when very young. It has a long tap root and sulks or bolts if disturbed. Sow it where it is to stay, or plant out small pot-grown seedlings without breaking the rootball.
Which parts can I eat?
All of them: leaves, stems, flowers, pollen, seeds and, in Florence fennel, the bulb.
What are the striped caterpillars on my fennel?
Probably swallowtail butterfly caterpillars, which are green with black bands and orange dots and feed on fennel and its relatives. They do little harm to a large plant; many gardeners leave them.
